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Science Is Durable
In spite of some well-known historical exceptions (the world is flat, the Earth
is the center of the solar system), most ideas in science tend to change rather
slowly and in small increments. The newer idea is usually a small variation
on the old one and tends to add rather than discard information. Our current
understanding is simply a refinement of the previous concept; one can follow
the evolution of the idea along a logical path. This idea is demonstrated in
forensic science by exactly the same example we used above to demonstrate
that science is dynamic. The methods that were originally used to include
each of these people in a class of individuals who could have perpetrated a
crime did not produce “wrong” results; repeated today (again barring cases
of intentional misrepresentation), they would provide exactly the same
answers. Rather, increasingly discriminating methods of detection enable us
to add knowledge to the previous results, allowing us to refine rather than
refute the answer. The two individuals with blood type “O” would still be
indistinguishable using that test; only with a more discriminating DNA test
are they differentiated. The critical distinction between these two kinds of
tests resides in the limitations inherent in each one. Qualified by the appro-
priate limitations, each conclusion remains valid.
 
d.
Forensic Science Is an Applied Science
The realm of science can be divided into pure science, or research, and applied
science. Basic research seeks to understand the physical world for its own
sake; in applied science we seek to use the physical principles discovered to
obtain a desired goal. Like medicine or engineering, the forensic analysis of
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8
Principles and Practice of Criminalistics
physical evidence is an applied science, resting firmly on a foundation of the
basic scientific principles of physics, chemistry, and biology. As such, every
experiment and every case must follow the scientific method of hypothesis
testing described above. It is worth clarifying that forensic casework is not
strictly experimental in nature. By definition, the conditions under which a
scientific experiment is performed are controlled, and variables are inten-
tionally changed one at a time; in casework, reality dictates that the sample
is completely uncontrolled until its recognition and recovery by a responsible